In one of his shortest video responses, Matt Cutts, the head of search spam at Google, answered the question:
Should I be worried if a couple of sites that I don't want to be associated with are linking to me?
He said as long as you disavow the links or the domain that has the links pointing to your site that you do not want to be associated with, then it will all be fine. He said, as long as you've taken those steps [disavow] then "I wouldn't worry."
Here is the video:
Matt did warn that when you do disavow, you should do so likely at the domain name like you would when you use a machete.
I am sure many webmasters have disavow and still didn't see much of a difference and there are plenty of reasons for that.
Forum discussion at Google+.
Image credit to BigStockPhoto for machete man